Myocardial Infarction (Heart Attack): Diagnostic Tests

From the first medical contact of a patient to the ECG diagnosis, a maximum of only ten minutes may pass! Obligatory medical device diagnostics

• Electrocardiogram (ECG; recording of the electrical activity of the heart muscle)* – during and after the occurrence of an infarction, in many cases it is evident on the ECG, primarily by ST-segment elevation [evidence of STEMI/ST segment elevation myocardial infarction; see below: “Stages of myocardial infarction on ECG”]. In rare cases: NSTEMI or unstable angina (“chest tightness”; sudden onset of pain in the cardiac region with inconstant symptoms) – no ST segment elevations; in NSTEMI, CK-MB and troponin (TnT) are elevated; in unstable angina, these values are within the normal range] For transient ST-segment elevation, see “Further notes” below.DD: In approximately 30% of patients with acute pancreatitis (inflammation of the pancreas), signs of posterior wall infarction can be detected on the ECG!Note:
  • Patients with NSTE-ACS (acute coronary syndrome) and defined risk features require invasive evaluation by coronary angiography.
  • In a person of non-Caucasian origin, ST-segment elevation on ECG above the ESC- or AHA/ACC-defined threshold should possibly be interpreted somewhat cautiously.
  • Myocardial infarction is often incorrectly assumed in patients with left bundle branch block on ECG-see “Further Considerations”: ECG Criteria in Left Bundle Branch Block.
• Blood pressure measurement* (both arms) [most important symptoms of IkS (infarct-related cardiogenic shock) – but not obligatory – hypotension/low blood pressure < 90 mmHG systolic for at least 30 minutes, in conjunction with signs of organ diminished perfusion/organ diminished blood flow: cold extremities, oliguria (decreased urine production with a daily maximum of 500 ml), mental changes such as agitation/sick agitation].
• Coronary angiography (radiological procedure that uses contrast agents to visualize the lumen (interior) of the coronary arteries (arteries that surround the heart in a wreath shape and supply the heart muscle with blood)) – to assess regional and global cardiac function, possibly with measurement of fractional flow reserve (FFR) to objectify the functional relevance of coronary stenoses; simultaneous therapy possible [from a patient’s first medical contact to ECG diagnosis a maximum of ten minutes and within 90 minutes of catheter intervention; in very early infarct onset (< 2 hours) and large anterior wall infarcts, the interval should be less than 60 minutes [Note: In approximately 7% of all myocardial infarctions, no relevant stenosis can be detected angiographically. ]Note: Patients with inconclusive ST elevation and atypical ECG changes (e.g., thigh blocks, ventricular paced rhythm, and isolated posterior myocardial infarction) should also receive early coronary angiography in the event of persistent ischemic symptoms.
• Echocardiography (echo; cardiac ultrasound) – can detect wall motion abnormalities (WBS) in the affected myocardial area (myocardium) and resultant ventricular dysfunction and is used when ECG could not provide definite findings in acute infarction or in chronic myocardial infarction (infarction occurred >3 months ago).
• Cardiac rhythm monitoring (NSTE-ACE guidelines, Management of Acute Coronary Syndrome without ST-segment elevation):
  • Until the diagnosis of NSTEMI can be either excluded or confirmed (Class 1 recommendation).
  • Consider for proven NSTEMI and low arrhythmic risk over 24 hours or until percutaneous coronary intervention (PCI) can be performed (Class IIa).
  • If arrhythmia risk is high, monitoring longer than 24 hours may be considered (class IIa)

Optional medical device diagnostics – depending on the results of the history, physical examination, laboratory diagnostics and obligatory medical device diagnostics – for differential diagnostic clarification or to exclude complications.

• X-ray of the chest (X-ray thorax/chest), in two planes – to exclude signs of decompensation, pulmonary congestion signs.
• Computed tomography of the thorax/chest (chest CT) – to exclude differential diagnoses in acute chest pain (chest pain).
• CT angiography (engl.Cardiac computed tomography angiography, (CCTA); noninvasive study to examine the patency of the coronary arteries).
  • For acute chest pain (chest pain) and low risk for acute coronary syndrome (ACS).
  • Suspected pulmonary embolism and aortic dissection (synonym: aneurysm dissecans aortae): acute splitting (dissection) of the wall layers of the aorta (aorta), with a tear of the inner layer of the vessel wall (intima) and a hemorrhage between the intima and the muscle layer of the vessel wall (outer media), in terms of an aneurysm dissecans (pathological expansion of the artery).
  • Patients in whom the primary aim is to exclude coronary artery disease (coronary artery disease) because of low to intermediate pretest probability; prerequisite: troponin values and/or ECG normal or equivocal (class I/evidence grade A recommendation) [guidelines: ESC Guidelines].
• Magnetic resonance imaging of the thorax/chest (chest MRI) – can detect myocardial dysfunction; not used in the acute setting.
• Myocardial perfusion scintigraphy – cannot distinguish between a fresh and an old infarct; performed to assess myocardial function
• Radionuclide ventriculography – performed to assess myocardial functional capacity.

* Infarct-induced cardiogenic shock (ICS), if ICS is suspected, see due tofurther diagnostics under “Shock”.

According to ECG manifestation, acute coronary syndrome (AKS; acute coronary syndrome, ACS) is classified as follows:

• Non-ST elevation
  • Unstable angina pectoris* (UA) or
  • NSTEMI* * – non-ST-elevation myocardial infarction. This type is smaller than a myocardial infarction with ST-segment elevation, but NSTEMI mostly affects high-risk patients with pre-damaged hearts. The long-term prognosis is also worse; or
  • NQMI – non-Q-wave myocardial infarction (NSTEMI); in 6 months, a Q-wave infarction occurs in about 30% of cases.
• ST elevation
  • STEMI* * – English ST-elevation myocardial infarction – myocardial infarction with ST-segment elevation.
    • QMI – Q-prong infarction
    • NQMI – Non-Q-wave myocardial infarction; in 6 months, Q-wave myocardial infarction occurs in approximately 30% of cases

* CK-MB and troponin (TnT) not elevated* * CK-MB and troponin (TnT) elevated.

Further notes

• Transient ST-segment elevation in acute coronary syndrome /4-24% of patients): TRANSIENT study concludes that these patients behave like NSTEMI patients; mircovascular obstruction is rare (4.2% versus 50% in STEMI patients):Patients with transient ST-segment elevation tend to be younger, frequent smokers, and majority male compared with STEMI patients.
• Patients with left bundle branch block (LBBB) on ECG are often misdiagnosed as having myocardial infarction. The BARCELONA criteria achieved the highest sensitivity (93%-95%) in both the evaluation and validation cohorts compared with previous criteria (eg, Sgarbossa score of ≥ 3: 33-34%). The three new criteria include:
  1. ST depression ≥ 0.1 mV (1 mm) concordant with QRS polarity (same direction as QRS) in all leads
  2. Excessive discordant ST deviation-that is, opposite to the direction of QRS-of ≥ 0.1 mV (1 mm) with low-voltage in QRS
  3. Concordant ST increase of ≥ 0.1 mV (1 mm) in any leads.

  If any of three points apply, myocardial infarction should be assumed.

Stages of myocardial infarction on ECG

Note: Unmasking of an acute posterior infarct becomes possible only in leads V7-V9; the same applies to right ventricular infarcts! Electrocardiographic definition of ST-elevation myocardial infarction (STEMI) (mod. after).